A capillary array DNA sequencer which collectively deciphers base sequences of different DNA samples in individual capillaries by performing electrophoretic analysis with in parallel processing using the plurality of capillaries (glass capillary each having an outer diameter of 100 μm to 400 μm and inner diameter of 25 μm to 100 μm) filled with a separation medium is widely used. This mechanism will be described later. A polyimide coating film is formed on an outer surface of a commercial capillary in order to preserve flexibility. A portion where an electrophoretic length of each capillary is constant, for example, a portion near a position of 30 cm distance away from a sample injection end of the capillary is arranged to be aligned on the same plane in a state where the coating film is removed and a laser beam is irradiated from a side of a capillary-array plane so as to simultaneously irradiate the plurality of capillaries with the laser beam. Hereafter, the capillary-array plane may be simply called a array plane in the present specification. A fluorescent labeled DNA, which is subjected to electrophoresis, inside each capillary described above emits fluorescence by being excited by laser irradiation when the DNA is passed across the laser beam. Here, DNA is labeled with fluorescent substances of four colors depending on the terminal base species of A, C, G, and T. As a result, laser-irradiation positions of respective capillaries become light-emitting points and a plurality of light-emitting points are arranged on a straight line at intervals of p. Hereafter, this is called a light-emitting-point array. When the number of the light-emitting points (number of capillaries) is set to n, the entire width W of the light-emitting-point array is W=p*(n−1). For example, when p=0.36 mm and n=24, W=8.28 mm. A fluorescence-detection system collectively detects respective light beams emitted from the light-emitting-point array while spectroscopically separating the light beams. A configuration of the system is illustrated in FIG. 3 of PTL 1.
First, respective emitted light beams are turned into parallel-light beams by a common condensing lens. Hereafter, an expression of “common” is used as the meaning (n-to-1 correspondence) that one optical element is used for a plurality of light-emitting points (n light-emitting points). In contrast, an expression of “individual” is used as the meaning (1-to-1 correspondence) that one optical element is used for one light-emitting point. Here, when a focal length of the common condensing lens is set as f and an effective diameter is set as D1, W<f and W<D1. For example, f=50 mm and D1=36 mm. Next, the parallel-light beams are allowed to be passed through a long pass filter so as to cut a wavelength of the laser beam and further allowed to be transmitted through a common transmission type diffraction grating so as to be subjected to wavelength dispersion in the long axis direction of each capillary, that is, the direction orthogonal to both the array direction of the light-emitting-point array and the optical axis of the common condensing lens. Here, when the effective diameter of the common transmission type diffraction grating is set as DG, it needs to be D1≤DG so as not to decrease detection efficiency. For example, DG=50 mm. Subsequently, the image of respective parallel-light beams formed on the two-dimensional sensor by the common imaging lens. Here, when the effective diameter of the common imaging lens is set as D2, it needs to be D1≤D2 so as not to decrease detection efficiency. For example, D2=36 mm. With matters as described above, it is possible to collectively acquire wavelength dispersion spectra of respective light beams emitted from the light-emitting-point array. Finally, temporal change in respective wavelength dispersion spectra is analyzed so as to obtain temporal change in intensity of fluorescence of four colors and determine the sequence of base species, that is, the base sequence.
Other means for simultaneously detect fluorescence of four colors is illustrated in FIG. 2 of NPL 1. First, light beam emitted from one light-emitting area is turned into parallel-light beam by one condensing lens (here, objective lens). Here, when the entire width of the light-emitting area is set as W, the focal length of the objective lens is set as f, and the effective diameter is set as D1, W<f and W<D1. The objective lens in use is UPLSAP0 60X W which is the Olympus's product, and W=0.44 mm, f=3 mm, and D1=20 mm. Next, the parallel-light beam is divided into four parallel-light beams of four colors by one set of three kinds of dichroic-mirrors. Subsequently, images of respective parallel-light beams are formed on four two-dimensional sensors by one set of four imaging lenses. Here, when the effective diameter of each imaging lens is set as D2, it needs to be D1<D2 so as not to decrease detection efficiency. With matters as described above, it is possible to collectively acquire four-divided images of four colors of the light-emitting area.
On the other hand, other means for simultaneously detect light beams emitted from the light-emitting-point array is illustrated in FIG. 1 of PTL 2. First, respective light beams emitted from the light-emitting-point array are turned into the parallel-light beams by an individual condensing-lens array. Here, when intervals between the light-emitting points is set as p and the number of light-emitting points is set as n, the entire width of the light-emitting-point array is W=p*(n−1), and when the effective diameter of each condensing lens is set as D1, D1<W. It is set that D1<p to thereby make it possible to set an individual condensing-lens array in which respective condensing lenses are aligned in a straight line. Next, respective parallel-light beams are made incident on respective individual sensors of the individual sensor array. With matters as described above, it is possible to collectively acquire intensities of light beams emitted from the light-emitting-point array.